1. Field of the Invention
The present invention relates to keyless chuck tightening and releasing mechanisms used in reversible electric drills and other reversible power tools which receive interchangeable work pieces.
2. Description of the Prior Art
Reversible power tools are currently used for many purposes throughout a wide variety of industries and in homes and businesses everywhere. One such implement which is widely used and which is found in many workshops is a portable, hand held reversible electric drill. Reversible electric drills typically have pistol shaped housings which may be held in one hand and operated by depression of a trigger. Within the housing there is an electric motor coupled in series with a switch operated by the trigger. The armature of the motor is geared to a drive shaft which protrudes from the nose of the pistol shaped housing. A drill chuck is fastened to the drill drive shaft.
The purpose of a drill chuck is to allow a user to selectively grip and release a variety of work pieces or drill bits. Such work pieces and drill bits have bases or stub axles which extend into a cavity in the drill chuck axially aligned with the drive shaft. A drill chuck includes a plurality of chuck jaws which may be radially advanced and retracted to grip a work piece or drill bit positioned in the chuck cavity. The chuck jaws are normally aligned at an angle relative to the drill drive shaft and are advanced both radially and axially relative to the drill drive shaft by means of a chuck jaw propulsion system.
The chuck jaw propulsion system is mounted for rotation relative to the chuck jaw guide and includes a threaded ring which interacts with corresponding threads on the chuck jaws to advance and retract the chuck jaws relative to the extended axis of rotation of the drill drive shaft.
During normal operation of the drill the chuck jaw propulsion or reciprocating mechanism and the jaw guide move together. That is, when power is applied to the drill the chuck jaw reciprocating mechanism and the jaw guide rotate together. If the chuck jaws grip a drill bit and power is applied to the drill, a relatively light axial force on the butt of the drill housing will provide the necessary pressure to allow the drill bit to bite into and bore a hole in an object to be drilled. The chuck jaws must grip the base of the drill bit tightly enough so that the resistance of the article to be drilled does not halt rotation of the drill bit and allow the chuck to rotate around the drill bit without turning the bit.
Conventional electric drills employ a key arrangement in order to tighten the chuck jaws sufficiently to firmly grip the drill bit in the chuck. Essentially the same chuck key tightening system has been used for many years on both reversible and unidirectional drills. According to this conventional chuck key tightening system the end of the chuck jaw propulsion structure is canted at an angle and is equipped with bevel gearing adjacent to the chuck jaw guide which it surrounds. The chuck jaw guide is equipped with blind radial wells oriented perpendicular to the axis of rotation of the drill drive shaft. A small chuck key has a stub axle extending from bevel gearing and includes a lever arm oriented radially outwardly from the axis of rotation of the bevel gearing. The stub axle of the chuck key is inserted into one of the blind wells in the chuck jaw guide, thereby bringing the bevel gearing of the chuck key and the corresponding bevel gearing on the chuck jaw propulsion structure into mating engagement. The chuck key extends perpendicular relative to the axis of rotation of the drill shaft when engaged with the chuck jaw guide and the chuck jaw propulsion system.
The chuck key can be rotated in a selection direction, thereby rotating the chuck propulsion structure about the axis of rotation of the drive shaft while preventing rotation of the chuck jaw guide. Rotation of the chuck jaw propulsion system and the relative immobilization of the chuck jaw guide will result in the chuck jaws advancing or retracting, depending upon the direction of rotation of the chuck jaw propulsion structure. A drill bit inserted between the chuck jaws can thereby be selectively gripped or released.
The chuck key is necessary both in the operation of removing a drill bit and in securement of another drill bit in the drill. However, the chuck key must be removed from engagement with the jaw guide and chuck jaw propulsion structure during drilling operations. If the chuck key is not removed, the drill can be seriously damaged and the user or observers are subjected to a considerable likelihood of injury by the chuck key.
The detachable nature of a conventional chuck key represents a serious disadvantage in the use of a drill. Chuck keys frequently become separated from the drill and misplaced. The absence of a chuck key is a constant source of irritation and frustration to users of a drill. While various types of leashes and chuck key constraining systems have been utilized to attempt to solve this problem, all previous devices of this type have proven unsatisfactory. Flexible chuck leashes frequently break and the drill key becomes separated from the drill. Rigid chuck key constraints also tend to malfunction and have the further disadvantage that engagement of the chuck key with both the chuck jaw guide and chuck jaw propulsion structure is not as readily apparent. Accordingly, the likelihood that the chuck key may be inadvertently left engaged so that damage or serious injury can occur is increased.
Some attempts have been made to devise systems which dispense with the requirement for a chuck key. For example, U.S. Pat. No. 2,716,555 discloses a system which utilizes the power of a reversible drill to tighten and loosen the chuck jaws without a chuck key. This system employs a slide which is directed radially toward the drive shaft of a drill and which is normally biased away from the drill drive shaft. The chuck jaw propulsion system is equipped with stop lugs extending radially outwardly within the drill housing. Depression of the slide against the radially outwardly spring bias operates the slide as a plunger to interfere with the radially extending stop lugs of the chuck jaw propulsion structure to immobilize that structure relative to the drill housing. With the chuck jaw propulsion structure immobilized, operation of the drill motor will turn the drill drive shaft, thereby rotating the chuck jaw guide as well. Depending upon the direction of rotation, the chuck jaws will be advanced or retracted to grip or release a drill bit located there between.
One problem with the system disclosed in U.S. Pat. No. 2,716,555 is that there is no mechanism for gradually immobilizing the chuck jaw propulsion system from rotation relative to the drill housing. The stop lugs always react with the slide to produce a sharp impact, thereby tending to damage the drill. Furthermore, there is no provision for automatically tightening and loosening the drill chuck jaws. The system must always be manually initiated. A further problem is that there is no provision for preventing overtightening of the chuck jaws on a drill bit. Because the force tending to tighten the chuck jaws upon the base of a drill bit is derived from the operation of the electric motor itself, the tightening force is very great. The chuck jaws can easily be driven so tightly about a drill bit that they cannot be loosened. While U.S. Pat. No. 2,716,555 does provide a clutch mechanism to disengage the drill drive shaft from the drive motor, no provision is made to allow release of a drill bit upon which the chuck jaws have been overtightened.